1. Field of the Invention
This invention relates to a method of and novel composition for use in joining refractory metal structures, and, more particularly, to the transient liquid phase bonding of such refractory metal structures.
2. Description of Related Art
Refractory metal structures may be employed as support structures in high temperature sintering furnaces known as sintering furniture or hardware. Oftentimes, the sintering furniture is made from molybdenum to withstand operating temperatures of up to 1700.degree. C. Occasionally, the sintering furniture breaks and must be repaired or discarded. Attempts at cost containment have led to methods of repairing the sintering furniture. Most preferably, repairing the sintering furniture achieves a defect free bond joint having a strength comparable to that of the sintering furniture itself.
Typically, repairs have been made by mechanically joining the broken pieces together. The mechanical joining process may comprise forming nubs on the one surface of the broken piece of sintering furniture and press fitting the nub into a drilled hole of the corresponding piece of furniture. However, due to the expansion and contraction of the pieces during thermal cycling of the furnace, the mechanical joint would fail. Thus, it would be desirable to join the broken pieces in a manner which is capable of sustaining the repeated thermal cycling of the furnace. A preferred manner of joining the structures would be a sintered joint which can withstand the thermal cycling and does not re-soften at the operating temperature of the furnace.
Transient liquid phase bonding has proven to be a very useful method in producing high quality bonds in high temperature metals. In transient liquid phase bonding, different metals of a eutectic system are deposited on the surfaces of the article to be bonded. It is desirable to find the system which produces a high quality joint while excluding from the interlayer alloy those elements which may adversely effect the bonding process or the quality of the resulting joint.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for joining refractory metal structures which provides a joint capable of withstanding repeated thermal cycling at extreme temperatures.
It is another object of the present invention to provide a method for joining molybdenum sintering furniture which provides a sintered joint capable of withstanding the repeated thermal cycling at extreme temperatures while not prone to re-melting or re-softening.
A further object of the invention is to provide a novel eutectic system for transient liquid phase bonding of refractory metal structures wherein the resulting joint does not contain elements which would substantially affect the bonding process or the quality of the joint.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.